U.S. patent number 8,219,106 [Application Number 11/221,329] was granted by the patent office on 2012-07-10 for reverse link load control.
This patent grant is currently assigned to Alcatel Lucent. Invention is credited to Martin H. Meyers, Alexandro Salvarani, Carl F. Weaver.
United States Patent |
8,219,106 |
Meyers , et al. |
July 10, 2012 |
Reverse link load control
Abstract
A reverse link load control strategy utilizes a total call load
metric in place of a reverse signal strength indicator metric for
managing reverse link resources. In a disclosed example, a load
control module (40) measures the reverse signal strength indicator
(62) and measures an active cell load (64) using known techniques.
A relationship between the reverse signal strength indicator, the
active cell load, an other cell load component and a jammer
component provides the ability to determine the other cell load
component and the jammer component. Once the other cell load
component has been determined, a total call load based upon the
active cell load component and the other cell load component
provides a useful metric for allocating reverse link resources
between existing users and for determining whether to allow a new
user, for example.
Inventors: |
Meyers; Martin H. (Montclair,
NJ), Salvarani; Alexandro (Edison, NJ), Weaver; Carl
F. (Morris Plains, NJ) |
Assignee: |
Alcatel Lucent (Paris,
FR)
|
Family
ID: |
37830638 |
Appl.
No.: |
11/221,329 |
Filed: |
September 7, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070054671 A1 |
Mar 8, 2007 |
|
Current U.S.
Class: |
455/453; 370/332;
455/115.2; 370/329; 455/452.2 |
Current CPC
Class: |
H04W
72/0486 (20130101); H04W 72/082 (20130101); H04W
28/02 (20130101) |
Current International
Class: |
H04W
72/00 (20090101); H04W 4/00 (20090101); H03C
1/62 (20060101) |
Field of
Search: |
;455/453,452.2,115.3,115.2 ;370/329,332 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Balaoing; Ariel
Attorney, Agent or Firm: Carlson, Gaskey & Olds PC
Claims
We claim:
1. A method of communicating, comprising using a base station
controller for: determining an active cell load of a reverse link
in a cell a plurality of times within a sampling period;
determining a reverse signal strength indicator (RSSI) a
corresponding plurality of times within the sampling period wherein
there is a time correlation between each determined active cell
load and a corresponding determined RSSI; determining an other cell
load component of interference associated with the reverse link for
the sampling period based upon (i) a first relationship that
includes an average of a thermal noise plus jammer component of the
interference during the sampling period if the active cell load is
above a selected threshold or (ii) a second, different relationship
that does not include the thermal noise plus jammer component for
determining the other cell load component if the active cell load
is below the selected threshold.
2. The method of claim 1, comprising determining a total call load
based on the determined other cell load component and the
determined active cell load component.
3. The method of claim 2, comprising determining whether to allow a
new call based upon the determined total call load.
4. The method of claim 2, comprising determining how to allocate
resources associated with the reverse link based upon the
determined total call load.
5. The method of claim 2, comprising determining a jammer component
of the interference based on the determined total call load and a
determined reverse signal strength indicator.
6. The method of claim 5, comprising determining the reverse signal
strength indicator using
RSSI.sub.i=N.sub.i.sup.TH+J.sub.i+RSSI.sub.i(X.sub.i.sup.act+X.sub.i.sup.-
oc) wherein RSSI is the reverse signal strength indicator; N.sup.TH
is a thermal noise component; J is the jammer component; X.sup.act
is the active cell load; and X.sup.oc is the other cell load
component.
7. The method of claim 5, comprising: determining the reverse
signal strength indicator and the active cell load at each of a
plurality of sample times; determining an average value of the
other cell load component for a period corresponding to the same
times; and determining an average value of the jammer component for
a period corresponding to the sample times.
8. The method of claim 7, comprising: determining the average
values by assuming the average values are constant during the
period and determining a minimum of: .times..function..times.
##EQU00010## wherein N.sup.TH+J is an average noise plus jammer
value; and X.sup.oc is an average other cell load component
value.
9. The method of claim 7, comprising: assuming the average value of
the jammer component remains constant during the period; and
determining a linear variation of the average value of the other
cell load component.
10. The method of claim 9, comprising determining the linear
variation by determining a minimum of:
.times..function..function..alpha..beta..function. ##EQU00011##
wherein .alpha. and .beta. are constants.
11. A method of communicating, comprising using a base station
controller for: determining an active cell load of a reverse link
in a cell, the active cell load being an amount of power received
at a base station from mobile stations that are power controlled by
the base station; determining an other cell load component of
interference associated with the reverse link. the other cell load
component being an amount of power received at the base station on
the reverse link from mobile stations that are not power controlled
by the base station; using the active cell load and the other cell
load component for determining how to allocate resources of the
reverse link; determining a reverse signal strength indicator; and
using a first time-dependent relationship between the reverse
signal strength indicator, the active cell load and the other cell
load component for determining the other cell load component if the
active cell load is above a threshold and using a second
time-dependent relationship between the reverse signal strength
indicator, the active cell load and the other cell load component
for determining the other cell load component if the active cell
load is below the threshold.
12. The method of claim 11, comprising determining the other cell
load component as a separate quantity from the active cell
load.
13. The method of claim 11, wherein determining the other cell load
component includes using a relationship that depends on determining
a jammer component of the interference for determining the other
cell load component.
Description
FIELD OF THE INVENTION
This invention generally relates to telecommunications. More
particularly, this invention relates to wireless
communications.
DESCRIPTION OF THE RELATED ART
Wireless communication systems are well known. Mobile stations,
such as cell phones, laptop computers or personal digital
assistants communicate with base stations that are part of a
wireless communication network. As known, base stations are
strategically placed to provide wireless communication coverage
over selected geographic areas. A variety of control mechanisms are
required to maintain useful and reliable communication between
mobile stations and base stations. One area where appropriate
control is required is maintaining the interference level on a
reverse link, which corresponds to a link from the mobile stations
to the base station, within acceptable levels to avoid interference
that would degrade the quality of service for mobile
subscribers.
One contribution to reverse link interference is the result of more
than one mobile station transmitting signals to a base station on
the carrier. This type of interference can be referred to as call
load interference.
Mobiles in wireless networks communicate with base stations by
transmitting on one of multiple frequency bands. The set of
frequency bands allocated for transmission is called the frequency
spectrum, which is owned by wireless service providers for
commercial use. In CDMA and UMTS wireless networks, mobiles
communicate with a base station by transmitting on a common
frequency band that is shared by many mobiles. This frequency band
is called the CDMA/UMTS carrier, and has the value of 1.25 MHz for
IS-95A/B, CDMA-2000, 3G1x EVDO and 3G1X EVDV and the value of 3.84
MHz for UMTS, for example.
As users are added to a carrier, or existing users transmit at
higher data lates in the same carrier, the level of interference
measured at the base station increases. An increase of RF
interference typically forces all active mobiles in the carrier to
transmit at a higher power to maintain the quality of service of
their respective links. Every time a new user is added, or a user
transmits at higher data rate, the average power transmission of
all the other users in the carrier increases to maintain their own
quality of service. Mobiles that are transmitting near their
maximum power suffer a degraded quality of service when new users
are added to the carrier, or existing users in the carrier increase
their rate of data transmission. This situation should be detected
and preferably avoided to control and minimize the rate of call
drops, maintain adequate data throughput to users, preserve the
quality of service perceived by the mobile users, and preserve the
reverse link coverage.
If the reverse link interference due to CDMA/UMTS mobiles increases
to very high values, generally the reverse link power control
mechanism becomes unstable. Small fluctuations in the reverse link
load in the carrier can generate large variations of the power
received at the base station. In the extreme case that too many
users are added to a carrier, the interference generates large
burst of errors in the reverse link transmissions, leading to loss
of data throughput and large amounts or retransmissions. In the
worst case it leads to call drops and discontinuity of service. For
instance, when the load is very high, admitting one more voice call
may generate enough increase in interference that existing mobiles
may drop their links to the base station because they cannot be
heard reliably.
The call load in the reverse link should be monitored continuously
and be maintained below safety margins to avoid instabilities
associated with large fluctuations in the power received at the
base station. This is typically done by measuring and comparing the
total power received at the base station against a threshold.
The process of controlling the reverse link RF interference is
called reverse link overload control, or "overload control." An
effective overload control requires accurate measurements of the
load at a high rate. In the case of reverse link high speed packet
data traffic, the same metric used by an overload control algorithm
to grant or deny access, is used to schedule the rate of packet
data users requesting RF resources. In the typical case, the
scheduler requires a relatively precise measurement of the load in
the whole range of the allowed load values. The overload control
algorithm, on the other hand, only need to know when the load is
near threshold or safety limit. Since the performance of the
scheduler depends on the ability to assign data rates very quickly
(on the order of 10 milliseconds, which is the minimum duration of
a frame to transmit packet data), the scheduler must receive an
accurate load metric at a rate of approximately 100 Hz in order to
assign the available RF efficiently.
An efficient overload control and packet data scheduler needs an
accurate call load metric at a high rate in order to utilize and
assign the available RF resources as efficiently as possible.
Failure to meet these requirements will degrade the performance of
the overload control and scheduler algorithms. This leads to
noticeable degradation of the link performance including reduced
user and carrier data throughputs, reduced capacity, large latency
in the data transmissions, call and sessions drops and
discontinuity of service.
Additionally, jammers such as non CDMA or UMTS sources of power
that contribute to the RF interference preferably will be dealt
with directly by the overload control and the scheduler. Jammers
will increase the interference at the base station but typically
should not be included in the load calculation because they do not
add to the instability of any interference. Therefore, an efficient
overload control and scheduler would preferably use a load metric
that is capable of measuring the jammer component in the total
interference.
The typical metric associated with reverse link loading is the
Reverse Signal Strength Indicator (RSSI). As it is well known, the
RSSI is not the metric of choice when allocating RF resources, but
it provides complementary knowledge of the reverse link RF
conditions. For example, when a jammer raises the RSSI and there
are no users in the carrier, the jammer may be high enough to bring
the RSSI above the blocking threshold in the carrier. If the
overload algorithm is based exclusively on the noise rise (RSSI
over thermal noise at the receiver), then users requesting RF
resources close to the base station will be blocked, even when
there is no load in the system and even if the user has sufficient
power to overcome the interference. In other words, failure to
measure the contribution of a jammer may lead to false alarms in
the overload control or underestimating of the rate assigned to
packet users. RSSI is not an ideal overload trigger, in part,
because it does not distinguish call load interference from jammer
interference.
Three main components contribute to the RSSI: thermal noise,
jammers and CDMAJUMTS traffic. The thermal noise is the background
level of interference present at the receiver in all the RSSI
measurements. This measurement usually remains constant during
operation of a cell, or at least for a long period of time when
compared to the life of a data transmission session. Jammers are
external sources of power that contribute to the RSSI but not to
the call load. Jammers can change their strength quickly but
typically remain constant for long periods of time. Jammers do not
respond to power control messages from cells. Examples of jammer
sources are "human made noise," or a GSM mobile transmitting in the
reverse link in a far cell in the same carrier but with a good path
loss to the base station. There is no known way to distinguish
thermal noise from jammers for purposes of overload or scheduling
control.
The call load component of RSSI, which results from CDMA/UMTS
traffic, is divided into two categories: the "active cell" (also
known as "same cell") interference and the "other cell"
interference. The "active cell" interference corresponds to the
amount of power received at the base station from mobiles that are
power controlled by the base station. Soft and softer handoff
mobiles are included in the active cell interference category. The
"other cell" interference is the amount of power from all the other
mobiles transmitting in the reverse link carrier that are power
controlled by neighbor base stations. These are not controlled by
the base station under observation.
In practice, only the call load associated with the "active cell"
traffic can be measured. One reason for using the RSSI as a metric
for reverse link load management instead of call load is that the
call load contribution from "other cells" typically can only be
measured using complex and costly-to-implement algorithms.
Conventional wisdom was that active call load and other cell load
were coupled or correlated. Simulations and testing have shown that
assuming a proportional relationship between the active and other
cell load is not accurate. This is a significant shortcoming
because the other cell term, which is only weakly correlated with
the active cell component, contributes to the increase in RF
instability of the carrier. The amount of other cell interference
can be large, and varies quickly with neighbor cell activity.
The total call load X.sup.total is a measure of the CDMA/UMTS RF
utilization in the reverse link. For a given sector i, the total
call load is given by
.di-elect cons..times..times..ident. ##EQU00001## where A.sub.i=the
set of all mobiles having an active set that contains sector i;
P.sub.cdma,i=total power measured at base station i due to all the
CDMA/UMTS mobiles transmitting in the carrier; I.sub.o,i=total
power spectral density measured at base station i in the CDMA/UMTS
carrier; W=CDMAJUMTS carrier bandwidth; E.sub.i,j=chip energy of
user j measured at base station i; X.sub.i.sup.act=active call load
measured in sector i due to all the active mobiles in sector i; and
X.sub.i.sup.oc="other cell" call load in sector i due to mobiles in
neighbor sectors of sector i
As defined in equation (1), the total call load is a dimensionless
quantity of range 0.ltoreq.X.sub.i.sup.total.ltoreq.1. A value of
zero means there are no CDMA/UMTS users in sector i. If the total
call load value is near 1, then most of the reverse link
interference in the carrier is due to CDMA/UMTS mobiles. In this
case the system is approaching the pole capacity condition. The
total call load can be separated into the sum of two components:
the active and the "other cell" call load as shown in equation (1).
Although both quantities can be measured at the base station, in
practice only the active component is directly measurable. The
"other cell" call load is difficult to determine, because it
requires the knowledge of all the user codes that are active in the
neighbor cells, which are not known by the base station in
observation. Therefore, only a lower bound of the total call load
is available, which is equal to the active call load in the
carrier.
Since the pole instability depends on the total call load and not
on the active call load alone, it is not sufficient to measure the
active call load to obtain an accurate metric for overload control
and reverse link scheduling. It would be desirable to be able to
determine the "other cell" call load component in order to be able
to obtain at least an estimate of the total call load.
If the call load metric is estimated incorrectly, or inaccurately,
only suboptimal tradeoffs can be achieved when assigning reverse
link data rates, while trying to maintain the quality of service
for existing users. A realistic model that computes the total call
load must take into account rapid variations of the "other cell"
interference. Attempts to ignore the "other cell" component in the
call load will invariably give an underestimation of the call load,
which will have to be compensated to protect the quality of service
of voice and data users. This will lead to a sub-optimal tradeoff
degrading the individual data throughput, and finally the sector
throughput performance. Therefore, there is a need for a reliable
method to determine the total call load including the important
"other cell" components.
SUMMARY OF THE INVENTION
This invention addresses the need for determining the total call
load on a reverse link. This invention also addresses the need for
determining a jammer component. With such information, better
overload control and better scheduling techniques become
possible.
A disclosed exemplary method of communicating includes determining
an other cell load component of interference on a reverse link.
One example includes determining a total call load based upon the
determined other cell load component and a determined active cell
load component.
One example includes determining a jammer component of the reverse
link interference based on the determined total call load and a
determined reverse signal strength indicator, using a relationship
between those components.
The various features and advantages of this invention will become
apparent to those skilled in the art from the following detailed
description. The drawings that accompany the detailed description
can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates selected portions of a wireless
communication system incorporating an embodiment of this
invention.
FIG. 2 is a flow chart diagram summarizing one example approach
consistent with an embodiment of this invention.
DETAILED DESCRIPTION
This invention provides an ability to accurately estimate or
determine the total call load X.sup.total at a high rate.
Additionally, this invention provides an ability to estimate or
determine the noise floor plus jammer (N.sub.0+J) contribution to
reverse link interference. These two quantities can strategically
be used as the input data for base station algorithms to manage the
reverse link RF resources in the air interface. The determined
total call load x.sup.total and noise floor plus jammer (N.sub.0+J)
metrics are useful for reverse link interference overload control,
scheduling and rate control of data users (e.g. packet data),
protecting reverse link coverage, detecting excessive cell
interference from neighbor sectors, estimating thermal noise floor,
and detecting and reporting external jammers in the carrier, for
example. With this invention, more accurate load determination and
scheduling is possible compared to previous systems that relied
upon RSSI as the control metric.
FIG. 1 schematically shows selected portions of an example wireless
communication system 20. A plurality of mobile stations 22, 24, 26
and 28 communicate with one or more base stations 30, 32. In the
illustrated example, the mobile station 22 is communicating with
the base station 30. The example mobile station 24 is in a softer
handoff mode switching between sectors that are both served by the
base station 30. The example mobile station 26 is in a soft handoff
mode between the base stations 30 and 32. The example mobile
station 28 is in communication with the base station 32.
The example base stations 30 and 32 include a reverse link load
control module 40 that includes suitable programming for monitoring
the interference level on a reverse link for a given carrier or
within a given sector. This description refers to reverse link load
control on a carrier. The principles associated with the disclosed
example are applicable to more than one carrier or an entire
sector. For discussion purposes, this description focuses on the
carrier example. Those skilled in the art who have the benefit of
this description will realize how the disclosed example is
applicable to interference load measurement and control for an
entire sector or an entire base station, for example.
The reverse link load control module 40 for the base station 30
performs various functions to determine an amount of interference
caused by a current call load and other factors that can influence
the amount of interference. In the illustrated example, the mobile
stations 22 and 24 are part of the active cell load component for a
carrier used by both mobile stations 22 and 24. In the same
example, the mobile station 26 is currently controlled by the base
station 32. The communications with the base station 30 during the
handoff mode are considered part of the active load component for
base stations 30 and 32 because the mobile station 26 is controlled
by the base stations 30 and 32 for purposes of power management,
for example.
In the illustrated example, the mobile station 28 does not
communicate intentionally with the base station 30. At the same
time, however, signals transmitted by the mobile station 28
schematically shown at 42 are being received at the base station 30
and constitute other cell interference and contribute to the total
call load of base station 30. Of course, the mobile station 28
contributes to the total call load of the base station 32.
The illustrated example also includes a jammer 50 that introduces
interference at the base station 30.
The load control module 40 is responsible for determining whether
to admit a new call and to schedule users for data transmission to
allocate resources on a given carrier, for example. In this
example, the load control module 40 utilizes a total call load
metric for making such decisions. This represents an improvement
over techniques that utilized a measured RSSI for the reasons
discussed above.
FIG. 2 includes a flow chart diagram 60 summarizing an example
approach for using a total call load metric. In this example, the
load control module 40 measures the reverse signal strength
indicator (RSSI) at 62. This is accomplished in one example using
known techniques. At 64, the load control module 40 measures the
active cell load component using known techniques. At 66, the load
control module 40 utilizes a derived relationship (Equation (2)
below) between the RSSI, the active cell load component, an other
cell load component and a jammer component to determine the other
cell load component and the jammer component. At 68, once the other
cell load component has been determined, the active cell load
component and the other cell load component are used to determine a
total call load for the carrier of interest.
The total call load, the jammer component, or both can then be
utilized to determine whether to admit a new call and how to
allocate current RF resources for existing users, for example.
The RSSI measured at a base station i is expressed in one example
in terms of four components: thermal noise N.sup.TH, jammer J,
active cell X.sup.act and other cell X.sup.oc:
.di-elect cons..times..times..times. ##EQU00002##
This example includes exploiting the above relationship between the
RSSI components for determining the values of the thermal noise
plus jammer component N.sub.i.sup.TH+J.sub.i and the "other cell"
load interference component X.sup.oc based on Equation (2) and
measurements of RSSI.sub.i and X.sub.i.sup.act. Once the "other
cell" load component is determined, the total call load
X.sub.i.sup.total=X.sub.i.sup.act+X.sub.i.sup.oc is known and can
be used as a significant and reliable input for overload control
and reverse link scheduler algorithms, for example.
One example includes determining an estimate of
N.sub.i.sup.TH+J.sub.i and X.sub.i.sup.oc using simultaneous
measurements of RSSI.sub.i and X.sub.i.sup.act. In one example,
RSSI is measured at baseband in the reverse link of the radio, and
X.sup.act is measured at the channel element ASIC using known
techniques. Sampling N sets of these measurements at a high rate,
such as every 1.25 msec for CDMA 2000 and every 1.67 msec for
1.times.EVDO, provides a time correlation between the active cell
load and RSSI over a period of the N samples. If the RSSI and
x.sub.i.sup.act are sampled fast, then the thermal noise plus
jammer term can be assumed constant in Equation (2) for the
duration of the N samples (i.e., the noise power can be assumed
constant and independent of time).
Equation (2) is solved in one example by assuming an average value
for the other cell load component X.sub.i in the time interval of
the N samples. In this case Equation (2) becomes:
RSSI.sub.i,j(1-X.sub.i,j.sup.act)= N.sub.i.sup.TH+J.sub.i
+RSSI.sub.i,j X.sub.i.sup.oc (3) where i=CDMA/UMTS carrier index
j=time sampling index, 1.ltoreq.j.ltoreq.N
N.sub.1.sup.TH+J.sub.i=average value of thermal noise plus jammer
power to be estimated in the N sample period X.sub.i.sup.oc=average
"other cell" load component in the N sample period.
For most cases, N=8 (i.e. 8 sample measurements are used to
minimize Equation (4)) is sufficient to obtain good accuracy. This
means accurate estimates of total call load and the noise plus
jammer component can be obtained every 10 milliseconds. Additional
IIR filtering techniques can be used to smooth the estimates, and
provide prediction values in future frames.
The average values over the sample period provides an ability to
determine the desired metric(s). In one example "determining" the
desired metric includes estimating it to a reasonable degree of
accuracy to render the metric reliable. This description includes
"estimating" as one example technique of "determining" a value. For
example, one determined other cell load component is an estimated
value.
The left hand side of Equation (3) is a known set of N values
measured at the base station i at N consecutive times. These values
are based on the measurements of the RSSI.sub.i and
X.sub.i.sup.act. On the right hand side of Equation (3), there are
two unknowns to be determined: the average thermal noise plus
jammer N.sub.i.sup.TH+J.sub.i and the average other cell call load
X.sub.i.sup.oc. In this example, the previously derived Equation
(2), which under the conditions stated above is valid, allows
obtaining an estimate of N.sub.i.sup.TH+J.sub.i and
X.sub.i.sup.oc.
In one example, Equation (3) is solved by assuming the following
linear model: N.sub.i.sup.TH+J.sub.i=constant in the N sample
interval; and X.sub.i.sup.oc=constant in the N sample interval. In
this case, the solution can be computed by minimizing the following
sum
.times..function..times. ##EQU00003## with solutions
.times..times..times..times..function..times..times..times..function..tim-
es..times. ##EQU00004## and
.times..function..times..times..times..function..times..times.
##EQU00005##
Another example includes solving Equation (2) using a linear model
for the time correlation of the other cell load component
X.sub.i.sup.oc. This example can be considered an enhancement model
to the constant other cell load model assumptions, because it
allows capturing quick changes of the other cell load for the
carrier during the observation period. The linear model of this
example accommodates linear changes in the other cell load during
the period containing the N samples. In this case the model
equations are given by: X.sub.i.sup.oc=constant in the N sample
interval; and X.sub.i,j.sup.oc=.alpha..sub.i+.beta..sub.i(j-1) with
1.ltoreq.j.ltoreq.N, where .alpha..sub.i and .beta..sub.i are
constant in the N sample interval.
In this example the average other cell load in the N sample period
is given by:
.times..times..alpha..beta..function. ##EQU00006## where
N.sub.i.sup.TH+J.sub.i, .alpha..sub.i and .beta..sub.i are the
three parameters obtained by minimizing the sum:
.times..function..function..alpha..beta..function. ##EQU00007##
This example involves the inversion of a 3.times.3 system of linear
equations. One difficulty in solving Equations (4) or (5) is when
there is no time correlation between the active call load and RSSI.
This occurs when X.sub.i.sup.act.apprxeq.0, (i.e., there are no
calls in the carrier). In this case it is not possible to separate
the other cell load from the thermal noise plus jammer terms. In
fact, the solution to Equations (4) or (5) when X.sub.i.sup.act is
small is given by N.sub.i.sup.TH+J.sub.i=0 and X.sub.i.sup.oc=1,
which corresponds to pole capacity and is incorrect. Accordingly,
in one example, when the measured values of
X.sub.i.sup.act.apprxeq.0, the solutions to Equations (2), (4) and
(5) are biased and are not used.
In one example, for values of X.sub.i.sup.act<0.4, the
correlations between the active call load and RSSI are too weak to
allow separating the other cell load X.sup.oc from the thermal
noise plus jammer N.sup.TH and J component in Equation (2). In this
example, if the measured active call load X.sub.i.sup.act<0.4
and assuming the thermal noise plus jammer power is kept constant
during the N samples period, the other cell load can be estimated
by using the fact that the standard deviation 6 of the "other cell"
interference power is proportional to the "other cell" interference
power: .sigma.[RSSI.sub.i
X.sub.i.sup.oc]=.sigma.[RSSI.sub.i(1-X.sub.i.sup.act)-N.sub.i.sup.TH-J.su-
b.i]=.sigma.[RSSI.sub.i(1-X.sub.i.sup.act)].apprxeq..kappa.E.sub.i.sup.oc
(6) where .kappa. is a constant and
.times..times..times..times..times. ##EQU00008##
The following equation provides an estimate for determining the
other cell load X.sup.oc when the active call load X.sup.act is
less than 0.4:
.apprxeq..sigma..times..times..function..kappa..times..times..times.
##EQU00009##
Given the determined estimate of the other cell load X.sup.oc, the
total call load X.sup.TOTAL is obtained using Equation (2), which
provides an estimate of the thermal noise plus jammer component
N.sub.i.sup.TH+J.sub.i.
The preceding description is exemplary rather than limiting in
nature. Variations and modifications to the disclosed examples may
become apparent to those skilled in the art that do not necessarily
depart from the essence of this invention. The scope of legal
protection given to this invention can only be determined by
studying the following claims.
* * * * *